1. Field of the Invention
The present invention relates to a color imaging element and an imaging apparatus, particularly to a color imaging element and an imaging apparatus capable of reducing generation of color moire and achieving high resolution.
2. Description of the Related Art
In a color imaging element of a single plate, since each pixel is provided with a unicolor color filter thereover, each pixel has only unicolor color information. Therefore, since the image which is output from the single-plate color imaging element is a RAW image (mosaic image), a multi-channel image is obtained by performing processing (synchronization processing) in which a missing color pixel is interpolated from a pixel in a surrounding area. In this case, there is a problem in a reproduction characteristic of a high-frequency image signal; i.e. compared to a monochrome imaging element, a color imaging element tends to cause an aliasing more easily in a taken image. Therefore, there is a critical problem to achieve a high resolution by increasing reproduction band while suppressing the occurrence of color moire (false color).
In a primary color Bayer arrangement, which is a color arrangement of color filters most widely used in a color imaging element of a single plate, since green (G) pixels are disposed checkerwise and pixels of red (R) and blue (B) are disposed line-sequentially, there is a problem of reproducibility degree when generating a high-frequency signal in an oblique direction for G-signal and in a horizontal direction and in a vertical direction for R-signal and B-signal.
When a monochrome vertically-striped pattern (high-frequency image) as shown in FIG. 23A enters a color imaging element which has color filters of Bayer arrangement as shown in FIG. 23B, the resultant images are as described below. That is, when the resultant images are compared for each color while sorting the images based on the color arrangement of the Bayer, R results in a thin flat image; B results in a dark flat image; and G results in a thin and dark mosaic color image as shown in FIGS. 23C to 23E, respectively. In the image, which is an originally monochrome image in which no concentration difference (level difference) occurs among R, G and B, the resultant image is colored depending on the color arrangement and the input frequency.
Likewise, when an image, which is a high-frequency oblique monochrome image as shown in FIG. 24A, enters an imaging element which has color filters of Bayer arrangement shown in FIG. 24B, the resultant images are as described below. That is, when the resultant images are compared for each color while sorting the images based on the color arrangement of the Bayer, R and B result in a thin flat color image; and G results in a dark flat color image as shown in FIGS. 24C to 24E. Assuming that the value of black is 0 and the value of white is 255, since only G is 255, the high-frequency monochrome oblique image results in a green image. As described above, the high-frequency oblique image cannot be correctly reproduced using the Bayer arrangement.
In an imaging apparatus which uses a color imaging element of a single plate, optical low-pass filter of a birefringent material such as a crystal is generally disposed in front of the color imaging element, thereby the problem is eliminated by optically reducing high-frequency waves. However, in this method, although the coloring due to a reflection of the high-frequency signal can be reduced, a problem is that the resolution is decreased accordingly.
In order to solve the above problems, there is proposed a color imaging element, in which a color filter arrangement of the color imaging element is configured in a three-color random array satisfying the following arrangement restriction conditions. That is, an arbitrary given pixel abuts on any one of three color pixels including a color of the given pixel at any one of four sides of the given pixel (Japanese Patent Application Laid-Open No. 2000-308080).
Also, there is proposed an image sensor (color imaging element), in which a color filter arrangement includes a plurality of filters each having different spectral sensitivity; and a first filter and a second filter are alternately disposed at a first predetermined cycle in one diagonal direction of a grid of pixel of the image sensor and alternately disposed at a second predetermined cycle in the other diagonal direction (Japanese Patent Application Laid-Open No. 2005-136766).
Further, there is proposed a color arrangement in color solid-state imaging elements (color imaging elements) of three primary colors of R, G and B, which is configured so that a set of 3 pixels of R, G and B are disposed flatly in a zigzag manner in a vertical direction to thereby uniform the appearance frequency of R, G and B; and an arbitrary line on an imaging area (flat line, vertical line and oblique line) passes through every color (Japanese Patent Application Laid-Open No. 11-285012).
Furthermore, there is proposed a color imaging element, in which R and B in three primary colors of R, G and B are disposed at intervals of 3 pixels in a horizontal direction and in a vertical direction; and G is disposed between the R and B (Japanese Patent Application Laid-Open No. 8-23543).